Receptor for advanced glycation end-products (RAGE) provides a link between genetic susceptibility and environmental factors in type 1 diabetes

Alpha cell receptor for advanced glycation end products associate with glucagon expression in type 1 diabetes

Hypoglycemia in type 1 diabetes associates with changes in the pancreatic islet α cells, where the receptor for advanced glycation end products (RAGE) is highly expressed. This study compared islet RAGE expression in donors without diabetes, those at risk of, and those with type 1 diabetes. Laser-dissected islets were subject to RNA bioinformatics and adjacent pancreatic tissue were assessed by confocal microscopy. We found that islets from type 1 diabetes donors had differential expression of the RAGE gene (AGER) and its correlated genes, based on glucagon expression. Random forest machine learning revealed that AGER was the most important predictor for islet glucagon levels. Conversely, a generalized linear model identified that glucagon expression could be predicted by expression of RAGE signaling molecules, its ligands and enzymes that create or clear RAGE ligands. Confocal imaging co-localized RAGE, its ligands and signaling molecules to the α cells. Half of the type 1 diabetes cohort comprised of adolescents and a patient with history of hypoglycemia-all showed an inverse relationship between glucagon and RAGE. These data confirm an association between glucagon and islet RAGE, its ligands and signaling pathways in type 1 diabetes, which warrants functional investigation into a role for RAGE in hypoglycemia.

Nanopore Sequencing of RAGE Gene Polymorphisms and Their Association with Type 2 Diabetes

The receptor for advanced glycation end products (RAGE) is a transmembrane protein that interacts with its ligands, advanced glycation end products (AGEs). AGEs are elevated in diabetes and diabetic complications, leading to increased oxidative stress and activation of pro-inflammatory pathways facilitated by AGE-RAGE signaling. Polymorphisms in the RAGE gene can potentially affect AGE-RAGE interaction and its downstream signaling, which plays a crucial role in the progression of diabetes and its complications. In this study, we used nanopore sequencing for genotyping of RAGE polymorphism and identified a maximum number of 33 polymorphisms, including two previously unreported novel mutations in a cohort of healthy, type 2 diabetics without nephropathy and type 2 diabetics with nephropathy in order to identify associations. Two novel RAGE polymorphisms in the intron 8 and 3'UTR region at genomic locations 32181834 and 32181132, respectively, were detected with a low frequency. For four previously reported polymorphisms, cross-validation by PCR-RFLP showed 99.75% concordance with nanopore sequencing. Analysis of genotype distribution and allele frequencies revealed that five single nucleotide polymorphisms, i.e., rs1800625, rs3131300, rs3134940, rs2070600, and rs9391855, were associated with an increased risk for type 2 diabetes.

Advanced Glycation End Products and Inflammation in Type 1 Diabetes Development

Type 1 diabetes (T1D) is an autoimmune disease in which the β-cells of the pancreas are attacked by the host's immune system, ultimately resulting in hyperglycemia. It is a complex multifactorial disease postulated to result from a combination of genetic and environmental factors. In parallel with increasing prevalence of T1D in genetically stable populations, highlighting an environmental component, consumption of advanced glycation end products (AGEs) commonly found in in Western diets has increased significantly over the past decades. AGEs can bind to cell surface receptors including the receptor for advanced glycation end products (RAGE). RAGE has proinflammatory roles including in host-pathogen defense, thereby influencing immune cell behavior and can activate and cause proliferation of immune cells such as islet infiltrating CD8+ and CD4+ T cells and suppress the activity of T regulatory cells, contributing to β-cell injury and hyperglycemia. Insights from studies of individuals at risk of T1D have demonstrated that progression to symptomatic onset and diagnosis can vary, ranging from months to years, providing a window of opportunity for prevention strategies. Interaction between AGEs and RAGE is believed to be a major environmental risk factor for T1D and targeting the AGE-RAGE axis may act as a potential therapeutic strategy for T1D prevention.

Soluble RAGE Prevents Type 1 Diabetes Expanding Functional Regulatory T Cells

Type 1 diabetes is an autoimmune disease with no cure, where clinical translation of promising therapeutics has been hampered by the reproducibility crisis. Here, short-term administration of an antagonist to the receptor for advanced glycation end products (sRAGE) protected against murine diabetes at two independent research centers. Treatment with sRAGE increased regulatory T cells (Tregs) within the islets, pancreatic lymph nodes, and spleen, increasing islet insulin expression and function. Diabetes protection was abrogated by Treg depletion and shown to be dependent on antagonizing RAGE with use of knockout mice. Human Tregs treated with a RAGE ligand downregulated genes for suppression, migration, and Treg homeostasis (FOXP3, IL7R, TIGIT, JAK1, STAT3, STAT5b, CCR4). Loss of suppressive function was reversed by sRAGE, where Tregs increased proliferation and suppressed conventional T-cell division, confirming that sRAGE expands functional human Tregs. These results highlight sRAGE as an attractive treatment to prevent diabetes, showing efficacy and reproducibility at multiple research centers and in human T cells.

Short Duration Alagebrium Chloride Therapy Prediabetes Does Not Inhibit Progression to Autoimmune Diabetes in an Experimental Model

Mechanisms by which advanced glycation end products (AGEs) contribute to type 1 diabetes (T1D) pathogenesis are poorly understood. Since life-long pharmacotherapy with alagebrium chloride (ALT) slows progression to experimental T1D, we hypothesized that acute ALT therapy delivered prediabetes, may be effective. However, in female, non-obese diabetic (NODShiLt) mice, ALT administered prediabetes (day 50-100) did not protect against experimental T1D. ALT did not decrease circulating AGEs or their precursors. Despite this, pancreatic β-cell function was improved, and insulitis and pancreatic CD45.1+ cell infiltration was reduced. Lymphoid tissues were unaffected. ALT pre-treatment, prior to transfer of primed GC98 CD8+ T cell receptor transgenic T cells, reduced blood glucose concentrations and delayed diabetes, suggesting islet effects rather than immune modulation by ALT. Indeed, ALT did not reduce interferon-γ production by leukocytes from ovalbumin-pre-immunised NODShiLt mice and NODscid recipients given diabetogenic ALT treated NOD splenocytes were not protected against T1D. To elucidate β-cell effects, NOD-derived MIN6N8 β-cell major histocompatibility complex (MHC) Class Ia surface antigens were examined using immunopeptidomics. Overall, no major changes in the immunopeptidome were observed during the various treatments with all peptides exhibiting allele specific consensus binding motifs. As expected, longer MHC Class Ia peptides were captured bound to H-2Db than H-2Kb under all conditions. Moreover, more 10-12 mer peptides were isolated from H-2Db after AGE modified bovine serum albumin (AGE-BSA) treatment, compared with bovine serum albumin (BSA) or AGE-BSA+ALT treatment. Proteomics of MIN6N8 cells showed enrichment of processes associated with catabolism, the immune system, cell cycling and presynaptic endocytosis with AGE-BSA compared with BSA treatments. These data show that short-term ALT intervention, given prediabetes, does not arrest experimental T1D but transiently impacts β-cell function.

Targeting the receptor for advanced glycation end products (RAGE) in type 1 diabetes

Type 1 diabetes (T1D) is one of the most common chronic diseases manifesting in early life, with the prevalence increasing worldwide at a rate of approximately 3% per annum. The prolonged hyperglycaemia characteristic of T1D upregulates the receptor for advanced glycation end products (RAGE) and accelerates the formation of RAGE ligands, including advanced glycation end products, high-mobility group protein B1, S100 calcium-binding proteins, and amyloid-beta. Interestingly, changes in the expression of RAGE and these ligands are evident in patients before the onset of T1D. RAGE signals via various proinflammatory cascades, resulting in the production of reactive oxygen species and cytokines. A large number of proinflammatory ligands that can signal via RAGE have been implicated in several chronic diseases, including T1D. Therefore, it is unsurprising that RAGE has become a potential therapeutic target for the treatment and prevention of disease. In this review, we will explore how RAGE might be targeted to prevent the development of T1D.

Pathological Implications of Receptor for Advanced Glycation End-Product (AGER) Gene Polymorphism

The receptor for advanced glycation end-products (RAGE) is a cell surface transmembrane multiligand receptor, encoded by the AGER gene. RAGE presents many transcripts, is expressed mainly in the lung, and involves multiple pathways (such as NFκB, Akt, p38, and MAP kinases) that initiate and perpetuate an unfavorable proinflammatory state. Due to these numerous functional activities, RAGE is implicated in multiple diseases. AGER is a highly polymorphic gene, with polymorphisms or SNP (single-nucleotide polymorphism) that could be responsible or co-responsible for disease development. This review was designed to shed light on the pathological implications of AGER polymorphisms. Five polymorphisms are described: rs2070600, rs1800624, rs1800625, rs184003, and a 63 bp deletion. The rs2070600 SNP may be associated with the development of human autoimmune disease, diabetes complications, cancer, and lung diseases such as chronic obstructive pulmonary disease and acute respiratory distress syndrome. The rs1800624 SNP involves AGER gene regulation and may be related to reduced risk of heart disease, cancer, Crohn's disease, and type 1 diabetes complications. The rs1800625 SNP may be associated with the development of diabetic retinopathy, cancer, and lupus but may be protective against cardiovascular risk. The rs184003 SNP seems related to coronary artery disease, breast cancer, and diabetes. The 63 bp deletion may be associated with reduced survival from heart diseases during diabetic nephropathy. Here, these potential associations between AGER polymorphisms and the development of diseases are discussed, as there have been conflicting findings on the pathological impact of AGER SNPs in the literature. These contradictory results might be explained by distinct AGER SNP frequencies depending on ethnicity.

The genetic architecture of type 1 diabetes mellitus

Type 1 diabetes mellitus (T1D) is a complex autoimmune disorder characterised by loss of the insulin-producing pancreatic beta cells in genetically predisposed individuals, ultimately resulting in insulin deficiency and hyperglycaemia. T1D is most common among children and young adults, and the incidence is on the rise across the world. The aetiology of T1D is hypothesized to involve genetic and environmental factors that result in the T-cell mediated destruction of pancreatic beta cells. There is a strong genetic risk to T1D; with genome-wide association studies (GWAS) identifying over 60 susceptibility regions within the human genome which are marked by single nucleotide polymorphisms (SNPs). Here, we review what is currently known about the genetics of T1D. We argue that advancing our understanding of the aetiology and pathogenesis of T1D will require the integration of genome biology (omics-data) with GWAS data, thereby making it possible to elucidate the putative gene regulatory networks modulated by disease-associated SNPs. This approach has a potential to revolutionize clinical management of T1D in an era of precision medicine.

The receptor for advanced glycation endproducts is a mediator of toxicity by IAPP and other proteotoxic aggregates: Establishing and exploiting common ground for novel amyloidosis therapies

Proteotoxicity plays a key role in many devastating human disorders, including Alzheimer's, Huntington's and Parkinson's diseases; type 2 diabetes; systemic amyloidosis; and cardiac dysfunction, to name a few. The cellular mechanisms of proteotoxicity in these disorders have been the focus of considerable research, but their role in prevalent and morbid disorders, such as diabetes, is less appreciated. There is a large body of literature on the impact of glucotoxicity and lipotoxicity on insulin-producing pancreatic β-cells, and there is increasing recognition that proteotoxicty plays a key role. Pancreatic islet amyloidosis by the hormone IAPP, the production of advanced glycation endproducts (AGE), and insulin misprocessing into cytotoxic aggregates are all sources of β-cell proteotoxicity in diabetes. AGE, produced by the reaction of reducing sugars with proteins and lipids are ligands for the receptor for AGE (RAGE), as are the toxic pre-fibrillar aggregates of IAPP produced during amyloid formation. The mechanisms of amyloid formation by IAPP in vivo or in vitro are not well understood, and the cellular mechanisms of IAPP-induced β-cell death are not fully defined. Here, we review recent findings that illuminate the factors and mechanisms involved in β-cell proteotoxicity in diabetes. Together, these new insights have far-reaching implications for the establishment of unifying mechanisms by which pathological amyloidoses imbue their injurious effects in vivo.

Effects of a Low Advanced Glycation End Products Diet on Insulin Levels: The Feasibility of a Crossover Comparison Test

Background

Advanced glycation end products (AGEs) are associated with diabetes mellitus. Digested food-derived AGEs have been implicated in the pathogenesis of AGE-related disorders, and restricting diet-derived AGEs improves insulin resistance in animal models. The AGE content in foods changes according to cooking method, and it is higher in baked or oven-fried foods than in those prepared by steaming or simmering. Here, we examined the feasibility of crossover comparison tests for determining how different cooking methods (normal diet vs. low-AGE diet) affect insulin levels in non-diabetic Japanese subjects.

Methods

Five adult men and women (age, 41 ± 7 years; body mass index (BMI), 21.7 ± 2.6 kg/m²) were enrolled. The following dietary regimen was used: days 1 - 3, control meal; day 4, test meal (normal diet vs. low-AGE diet); day 5, washout day; and day 6, test meal. On days 4 and 6, blood samples were collected before and at 2, 4, and 6 h after meals.

Results

Blood levels of N-(carboxymethyl) lysine (CML) increased with dietary intake, but the increase was similar for the normal diet and low-AGE diet groups. Mean plasma glucose, insulin, triglycerides (TG), and CML did not differ significantly between the two groups. The area under the curve (AUC) for insulin levels was lower in the low-AGE diet group (d = 0.8). The sample size calculated from the effect size of the insulin AUC change was 22.

Conclusions

Twenty-two subjects may be needed to investigate the changes in clinical parameters attributable to cooking method in non-diabetic Japanese subjects.

Genetic variants in the receptor for advanced glycation end products (RAGE) gene were associated with circulating soluble RAGE level but not with renal function among Asians with type 2 diabetes: a genome-wide association study

Background

The soluble receptor for advanced glycation end products (sRAGE) has been shown to play an important role in diabetic complications. We conducted genome-wide association study (GWAS) of sRAGE in Asian type 2 diabetes mellitus (T2DM) patient and validated the association in an independent cohort of T2DM.

Methods

GWAS for sRAGE was performed in 2058 T2DM patients. Associations between single-nucleotide polymorphisms (SNPs) and plasma sRAGE level were analyzed in an additive model using a linear mixed model. To validate the associations, we performed de novo genotyping in an independent cohort (n = 1984). We selected the top SNP for assessment with diabetic kidney disease (DKD).

Results

The strongest SNP, rs2070600C>T (P = 1.21 × 10-52), was a genotyped, missense SNP located on chromosome 6, corresponding to the RAGE (AGER) gene locus, the gene encoding RAGE. Conditioning analysis on rs2070600 revealed that rs2071288C>T was the top genotyped independent SNP (P = 8.36 × 10-10). Both SNPs were strongly and dose-dependently correlated with sRAGE level (TT = 399.6 pg/mL, CT = 737.0 pg/mL and CC = 967.0 pg/mL, P < 0.001 for rs2070600; TT = 687.9 pg/mL, CT = 737.6 pg/mL and CC = 904.7 pg/mL, P < 0.001 for rs2072188). Both SNPs were robustly replicated in the independent cohort, especially among Chinese patients (P = 9.02 × 10-72 for rs2070600; P = 1.13 × 10-9 for rs2071288). Log-transformed sRAGE was associated with DKD after adjustment for age, gender and ethnicity in pooled cohorts [odds ratio 2.536 (95% confidence interval 1.864-3.450), P < 0.001]. However, we did not observe any significant association between rs2070600 and DKD.

Conclusions

Common variants in RAGE are strongly associated with plasma sRAGE level, which is associated with DKD. However, we did not find a causal link between sRAGE and renal function by Mendelian randomization.

Deficiency of S100B confers resistance to experimental diabetes in mice

The calcium binding protein S100B has been implicated in diabetic neuronal and vascular complications but has not been examined in the development of diabetes. S100B knock out (S100B KO) and wild-type (WT) mice were injected with 40 mg/kg body weight streptozotocin (STZ) for 5 days. Blood and pancreatic tissue samples were obtained to examine islet structure and function, the profile of glucose and insulin and expression of glucose transporter 2 (Glut2), S100B and its receptor, the receptor for advanced glycation end products (RAGE). Primary islet β-cells cultures from WT mice were used to test the apoptotic potential of S100B. S100B KO mice were resistant to STZ induced-diabetes with lower urine volume, food and water intake compared to WT mice. S100B increased in the WT islet following diabetes but did not co-localize with beta or peri-islet Schwann cells but with CD3 + T lymphocytes. S100B KO mice exhibited enhanced glucose tolerance, insulin sensitivity, prevented β-cell destruction and functional impairment in response to STZ treatment. S100B deficiency was associated with decreased Glut2 and RAGE. In primary β-cell cultures from WT mice, S100B induced reactive oxygen species (ROS) and RAGE-dependent apoptosis. In the STZ diabetic animal model, abrogation of S100B enhances insulin sensitivity and reduces pancreatic islet, and β-cell destruction. S100B may be a promising target for pharmacological interventions aimed at repressing diabetes.

Pancreatic islet inflammation: an emerging role for chemokines

Both type 1 and type 2 diabetes exhibit features of inflammation associated with alterations in pancreatic islet function and mass. These immunological disruptions, if unresolved, contribute to the overall pathogenesis of disease onset. This review presents the emerging role of pancreatic islet chemokine production as a critical factor regulating immune cell entry into pancreatic tissue as well as an important facilitator of changes in tissue resident leukocyte activity. Signaling through two specific chemokine receptors (i.e., CXCR2 and CXCR3) is presented to illustrate key points regarding ligand-mediated regulation of innate and adaptive immune cell responses. The prospective roles of chemokine ligands and their corresponding chemokine receptors to influence the onset and progression of autoimmune- and obesity-associated forms of diabetes are discussed.

A drop in the circulating concentrations of soluble receptor for advanced glycation end products is associated with seroconversion to autoantibody positivity but not with subsequent progression to clinical disease in children en route to type 1 diabetes

BACKGROUND

Advanced glycation end products (AGEs) and their interaction with the receptor for AGEs (RAGE) have been studied for their role in the pathogenesis and complications of type 1 diabetes. Decreased concentrations of soluble RAGE (sRAGE) have been reported in acute autoimmune inflammation. We set out to analyze the changes in sRAGE concentration during preclinical diabetes in children seroconverting to islet autoantibody positivity.

METHODS

We measured serum concentrations of sRAGE in 168 children who progressed to clinical disease and 43 children who turned positive for at least 2 diabetes-associated autoantibodies but remained nondiabetic. We analyzed the sRAGE before seroconversion in the first autoantibody-positive sample and annually thereafter until the diagnosis of type 1 diabetes or end of follow-up.

RESULTS

Both groups had similar sRAGE before seroconversion, but subsequently, sRAGE concentrations were lower (P < .001) in the progressors. The progressors had significantly higher sRAGE concentrations before than after seroconversion (P < .001). The nonprogressors did not experience a similar decrease. The sRAGE concentrations remained stable after seroconversion in both groups.

CONCLUSIONS

These data indicate that sRAGE may be involved in the initiation of beta-cell autoimmunity but not in the progression from beta-cell autoimmunity to clinical disease.

Receptor for Advanced Glycation End Products (RAGE) in Type 1 Diabetes Pathogenesis

The receptor for advanced glycation end products (RAGE) is a novel protein increasingly studied in the pathogenesis of type 1 diabetes (T1D). RAGE is expressed by several immune cell types, including T cells, antigen-presenting cells, endothelial cells, and the endocrine cells of the pancreatic islets. RAGE binds various ligands including advanced glycation end products (AGEs), high-mobility group box protein 1 (HMGB1), S100 proteins, β-amyloid, β-sheet fibrils, and lipopolysaccharide. AGEs are a particularly interesting ligand because their exogenous introduction into the body can be accelerated by the consumption of AGE-rich processed foods. This review will detail RAGE isoforms and its ligands and discuss how RAGE binding on the aforementioned cells could be linked to T1D pathogenesis.

Dietary factors in the development of type 1 diabetes

There are several indicators concerning the putative importance of dietary factors during the fetal period lactation, infancy and childhood in the etiology of type 1 diabetes. Among foods, cow's milk consumption has been associated with an increased risk of preclinical and/or clinical type 1 diabetes and sugars with a progression from preclinical to clinical disease. Breast milk, on the other hand, may be protective. Processed foods may be related to a greater risk of type 1 diabetes because they contain higher amounts of advanced glycation end-products. Nitrites or N-nitroso compounds in processed meat products could increase the risk of this disease. Among nutrients, n-3 fatty acids, vitamins D and E, and zinc may protect from preclinical and/or clinical type 1 diabetes. The microbial composition of foods or food's other effects on gut microbiota are receiving increasing attention, also due to their putative role in the development of type 1 diabetes. Still the number of prospective studies in this research field is limited and most of the findings remain to be replicated.

Functional promoter polymorphisms of the receptor for advanced glycation end products in children and adolescents with type 1 diabetes

RAGE promoter polymorphisms are associated with increases in RAGE expression. A case-control association study was conducted involving a Euro-Brazilian population of children and adolescents with type 1 diabetes (n = 90) and healthy controls (n = 105), which were matched by sex and age. Genotyping by PCR-RFLP the -429T>C (rs1800625), -374T>A (rs1800624), and 63 bp deletion/insertion (-407 to -345 bp) showed no significant differences (P > 0.05) between the groups.

Dietary Advanced Glycation End Products Consumption as a Direct Modulator of Insulin Sensitivity in Overweight Humans: A Study Protocol for a Double-Blind, Randomized, Two Period Cross-Over Trial

BACKGROUND

Advanced glycation end products (AGEs) are formed during the processing, storage, and cooking of foods. As part of a western diet, AGEs are consumed in excess and impair glucose metabolism in patients with type 2 diabetes. In the absence of diabetes, AGE-mediated decreases in insulin sensitivity and signaling have been postulated. However, randomized studies to test this relationship in humans are limited.

OBJECTIVE

The primary aim of this trial is to determine whether dietary consumption of AGEs will decrease insulin sensitivity in healthy overweight adults. A secondary aim is to determine the effects of dietary AGEs on insulin secretion, circulating soluble receptor for AGEs (sRAGE), and inflammation markers.

METHODS

Overweight, but otherwise healthy, non-diabetic adults (N=20) aged 18-50 years old will complete a randomized cross-over design intervention study alternating low and high (4-fold increase) AGE diets (2-week duration). At baseline, participants will undergo a medical review including an intravenous glucose tolerance test (IVGTT), a hyperinsulinemic-euglycemic clamp, and anthropometric measures and questionnaires assessing diet, physical activity, and general wellness. Each test diet will be followed for 14 days, followed by a 4-week washout period before commencement of the second alternate dietary period. Energy, macronutrient, and AGE intake will be calculated for each dietary period. Additionally, the AGE content of foods used in the study will be measured by ultra performance liquid chromatography mass spectrometry. All measurements will be repeated at the beginning and end of each dietary period. Primary and secondary outcomes will be expressed as a change over the dietary period for insulin sensitivity, secretion, anthropometric parameters, sRAGE, and inflammation markers and compared by paired t test and analysis of variance (ANOVA).

RESULTS

The study will be completed in early 2016.

CONCLUSION

The proposed trial will provide much needed clinical evidence on the impact of excess dietary AGE consumption on insulin sensitivity and will indicate whether lowering dietary AGE intake can improve insulin sensitivity and/or secretion, thereby decreasing risk for type 2 diabetes.

TRIAL REGISTRATION

Clinicaltrials.gov NCT00422253; https://clinicaltrials.gov/ct2/show/NCT00422253 (Archived by Webcite at http://www.webcitation.org/6ZXLhT89c).

Soluble RAGEs - Prospects for treating & tracking metabolic and inflammatory disease

Emerging evidence links the receptor for advanced glycation endproducts (RAGE) to the pathogenesis of tissue damage in chronic metabolic and inflammatory diseases. In human subjects, multiple reports suggest that in the plasma/serum, circulating levels of distinct forms of soluble RAGEs may be biomarkers of the presence or absence, and the extent of chronic disease. These considerations prompt us to consider in this review, what are soluble RAGEs; how are they formed; what might be their natural functions; and may they serve as biomarkers of inflammatory and metabolic disease activity? In this brief review, we seek to address what is known and suggest new areas for scientific investigation to uncover the biology of soluble RAGEs.

Genetics of Plasma Soluble Receptor for Advanced Glycation End-Products and Cardiovascular Outcomes in a Community-based Population: Results from the Atherosclerosis Risk in Communities Study

Plasma soluble Receptor for Advanced Glycation End-products (sRAGE) is a strong marker of vascular outcomes although evidence on the direction of association is mixed. Compared to whites, blacks have lower levels of sRAGE. We hypothesized that genetic determinants of sRAGE would help clarify the causal role of sRAGE and the black-white difference in sRAGE levels. We conducted a genome-wide analysis of sRAGE in whites and blacks from the Atherosclerosis Risk in Communities Study. Median plasma sRAGE levels were lower in blacks than whites (728 vs. 1067 pg/ml; P<0.0001). The T (vs. C) allele of rs2070600, a missense variant in AGER, the gene encoding RAGE, was associated with approximately 50% lower sRAGE levels in both whites (N = 1,737; P = 7.26x10^-16; minor allele frequency (MAF) = 0.04) and blacks (N = 581; P = 0.02; MAF = 0.01). In blacks, the T (vs. C) allele of rs2071288, intronic to AGER, was associated with 43% lower sRAGE levels (P = 2.22x10^-8; MAF = 0.10) and was nearly absent in whites. These AGER SNPs explained 21.5% and 26% of the variation in sRAGE in blacks and whites, respectively, but did not explain the black-white difference in sRAGE. These SNPs were not significantly associated with incident death, coronary heart disease, diabetes, heart failure, or chronic kidney disease in whites (N = 8,130–9,017) or blacks (N = 2,293–2,871) (median follow up ~20 years). We identified strong genetic determinants of sRAGE that did not explain the large black-white difference in sRAGE levels or clearly influence risk of clinical outcomes, suggesting that sRAGE may not be a causal factor in development of these outcomes.

Decrease in circulating concentrations of soluble receptors for advanced glycation end products at the time of seroconversion to autoantibody positivity in children with prediabetes

OBJECTIVE

Dietary advanced glycation end products (AGEs) and their interactions with the receptor for AGEs (RAGE) may play a role in the pathogenesis of type 1 diabetes. This study set out to assess whether there is any association of circulating concentrations of soluble RAGE (sRAGE), AGEs, and their ratio with the appearance of diabetes-associated autoantibodies in children progressing to clinical diabetes.

RESEARCH DESIGN AND METHODS

Serum concentrations of sRAGE, N-ε(carboxymethyl)lysine (CML) adducts, and the sRAGE/CML ratio were analyzed in children who progressed to type 1 diabetes. The samples were taken at four time points: before seroconversion, at the time of the first autoantibody-positive sample, at the time of the first sample positive for multiple (>2) autoantibodies, and close to the disease diagnosis. Samples of autoantibody-negative controls matched for age, sex, and HLA-conferred diabetes risk were analyzed at corresponding time points.

RESULTS

The prediabetic children had higher sRAGE concentrations before seroconversion (Pc = 0.03), at the appearance of multiple autoantibodies (Pc = 0.008), and close to diagnosis (Pc = 0.04). Close to diagnosis, the cases had lower CML concentrations than the controls (Pc = 0.004). Prediabetic children had a higher sRAGE/CML ratio than the controls before seroconversion (Pc = 0.008) and at diagnosis (Pc < 0.001).

CONCLUSIONS

Prediabetic children have higher concentrations of sRAGE and a higher sRAGE/CML ratio than healthy controls. Circulating sRAGE concentrations seem to decline with the appearance of diabetes-predictive autoantibodies in children progressing to type 1 diabetes. The higher sRAGE/CML ratio in prediabetic children may reflect a higher AGE scavenger capacity.

Relationship of Soluble RAGE with Insulin Resistance and Beta Cell Function during Development of Type 2 Diabetes Mellitus

This study examined whether circulating levels of soluble receptor for advanced glycation end products (sRAGE) alter in prediabetes and correlate with insulin resistance (IR) and beta cell function in prediabetes and newly diagnosed type 2 diabetes mellitus (T2DM). Subjects without previous history of diabetes were recruited and grouped as control, prediabetes, and newly diagnosed T2DM. The control subjects (n = 40) and people with prediabetes (n = 52) and diabetes (n = 66) were similar in terms of age, sex, BMI, systolic and diastolic BP, and fasting insulin level. HOMA-IR was found significantly higher in people with diabetes than control subjects (p < 0.001) and people with prediabetes (p = 0.005); and HOMA-%B was found significantly deteriorated in people with diabetes (p < 0.001) compared to control subjects and people with prediabetes. However, serum sRAGE levels did not show any significant alteration in people with prediabetes compared to control subjects. Moreover, univariate and multivariate analyses did not identify any significant correlation and statistical association of sRAGE with HOMA-IR and HOMA-%B in people with prediabetes and newly diagnosed T2DM. Our data suggest that serum sRAGE levels do not alter in people with prediabetes compared to control subjects and do not correlate or associate with IR and beta cell function during development of T2DM.

Circulating concentrations of soluble receptor for AGE are associated with age and AGER gene polymorphisms in children with newly diagnosed type 1 diabetes

OBJECTIVE

We analyzed the relationship among soluble receptor for advanced glycation end products (sRAGEs), the clinical phenotype, HLA genotype, and risk-associated single nucleotide polymorphisms (SNPs) in the AGER gene in a large population of Finnish children with newly diagnosed type 1 diabetes.

RESEARCH DESIGN AND METHODS

Samples from 2,115 clinically phenotyped children <15 years of age in whom type 1 diabetes was diagnosed and 316 control subjects were analyzed for sRAGEs. Three SNPs of AGER, previously associated with HLA-DR/DQ haplotype independent diabetes risk (rs2070600, rs9469089, and rs17493811), were analyzed in 1,390 affected subjects.

RESULTS

Children with type 1 diabetes and control subjects had similar sRAGE concentrations (1,171 vs. 1,153 pg/mL, P = 0.48). There was a correlation between age at diagnosis and serum sRAGE concentrations (r = 0.10, P < 0.001) among the patients but not among the control subjects. Children <2 years of age had the lowest concentrations in the diabetic population (1,027 vs. 1,181 pg/mL, P < 0.001) and the highest among the control subjects (1,329 vs. 1,140 pg/mL, P = 0.04). Ketoacidosis at diagnosis was associated with reduced concentrations (1,086 vs. 1,190 pg/mL, P < 0.001). HLA DR3/DR4 heterozygosity and the DR3 allele were associated with reduced sRAGE concentrations. The predisposing AA genotype of rs2070600 was associated with decreased sRAGE concentrations, while the protective CC genotype of rs9469089 was linked to increased concentrations.

CONCLUSIONS

Age and AGER polymorphisms are associated with the circulating sRAGE concentration among children with type 1 diabetes. The observations of reduced sRAGE concentrations in young children, in those with ketoacidosis, and in carriers of the high-risk HLA DR3/DR4 genotype suggest that decreased sRAGE concentration reflects a more aggressive disease phenotype.

The relationship between RAGE gene four common polymorphisms and breast cancer risk in northeastern Han Chinese

We aimed to evaluate the association of four common polymorphisms (rs1800625, rs1800624, rs2070600, and rs184003) in receptor for advanced glycation end products (RAGE) gene to evaluate their epistatic influence on breast cancer risk in northeastern Han Chinese. This is a hospital-based case-control study involving 509 histologically-proven breast cancer patients and 504 cancer-free controls. The genotype and allele distributions of rs184003 differed significantly between patients and controls, even after the Bonferroni correction. Individuals carrying the rs184003 T allele exhibited 1.62-fold increased risk of breast cancer (odds ratio (OR) = 1.62; 95% confidence interval (95% CI): 1.26–2.08; P < 0.001) after adjusting for confounders. The frequency of haplotype T-T-G-T (alleles in order of rs1800625, rs1800624, rs2070600, and rs184003) was remarkably higher in patients than in controls (Simulated P = 0.001), and this haplotype was significantly associated with a 1.43-fold (95% CI: 1.01–2.01; P = 0.041) increase in adjusted risk of breast cancer. Further analysis indicated that there was synergistic interaction between rs184003 and rs2070600, whereas their joint information gain value was relatively small (0.27%). Taken together, although there was no suggestive evidence for the presence of epistasis in RAGE gene, our findings clearly demonstrate that rs184003 might play a predominant role in the development of breast cancer.

Systemic soluble receptor for advanced glycation endproducts is a biomarker of emphysema and associated with AGER genetic variants in patients with chronic obstructive pulmonary disease

RATIONALE

Emphysema in chronic obstructive pulmonary disease (COPD) can be characterized by high-resolution chest computed tomography (HRCT); however, the repeated use of HRCT is limited because of concerns regarding radiation exposure and cost.

OBJECTIVES

To evaluate biomarkers associated with emphysema and COPD-related clinical characteristics, and to assess the relationships of soluble receptor for advanced glycation endproducts (sRAGE), a candidate systemic biomarker identified in this study, with single-nucleotide polymorphisms (SNPs) in the gene coding for RAGE (AGER locus) and with clinical characteristics.

METHODS

Circulating levels of 111 biomarkers were analyzed for association with clinical characteristics in 410 patients with COPD enrolled in the TESRA study. sRAGE was also measured in the ECLIPSE cohort in 1,847 patients with COPD, 298 smokers and 204 nonsmokers. The association between 21 SNPs in the AGER locus with sRAGE levels and clinical characteristics was also investigated.

MEASUREMENTS AND MAIN RESULTS

sRAGE was identified as a biomarker of diffusing capacity of carbon monoxide and lung density in the TESRA cohort. In the ECLIPSE cohort, lower sRAGE levels were associated with increased emphysema, increased Global Initiative for Chronic Obstructive Lung Disease stage, and COPD disease status. The associations with emphysema in both cohorts remained significant after covariate adjustment (P < 0.0001). One SNP in the AGER locus, rs2070600, was associated with circulating sRAGE levels both in TESRA (P = 0.0014) and ECLIPSE (7.07 × 10(-16)), which exceeded genome-wide significance threshold. Another SNP (rs2071288) was also associated with sRAGE levels (P = 0.01) and diffusing capacity of carbon monoxide (P = 0.01) in the TESRA study.

CONCLUSIONS

Lower circulating sRAGE levels are associated with emphysema severity and genetic polymorphisms in the AGER locus are associated with systemic sRAGE levels. Clinical trial registered with www.clinicaltrials.gov (NCT 00413205 and NCT 00292552).

Advanced glycation end products (AGEs) are cross-sectionally associated with insulin secretion in healthy subjects

It has been postulated that chronic exposure to high levels of advanced glycation end products (AGEs), in particular from dietary sources, can impair insulin secretion. In the present study, we investigated the cross-sectional relationship between AGEs and acute insulin secretion during an intravenous glucose tolerance test (IVGTT) and following a 75 g oral glucose tolerance test (OGTT) in healthy humans. We report the cross-sectional association between circulating AGE concentrations and insulin secretory function in healthy humans (17 F: 27 M, aged 30 ± 10 years) with a wide range of BMI (24.6-31.0 kg/m(2)). Higher circulating concentrations of AGEs were related to increased first phase insulin secretion during IVGTT (r = 0.43; p < 0.05) and lower 2-h glucose concentrations during OGTT (r = -0.31; p < 0.05). In addition, fasting (r = -0.36; p < 0.05) and 2-h glucose concentrations were negatively related to circulating levels of soluble receptor for AGE (RAGE) isoforms (r = -0.39; p < 0.01). In conclusion, in healthy humans, we show a cross-sectional association between advanced glycation end products and acute insulin secretion during glucose tolerance testing.

Mechanisms of diabetic complications

It is increasingly apparent that not only is a cure for the current worldwide diabetes epidemic required, but also for its major complications, affecting both small and large blood vessels. These complications occur in the majority of individuals with both type 1 and type 2 diabetes. Among the most prevalent microvascular complications are kidney disease, blindness, and amputations, with current therapies only slowing disease progression. Impaired kidney function, exhibited as a reduced glomerular filtration rate, is also a major risk factor for macrovascular complications, such as heart attacks and strokes. There have been a large number of new therapies tested in clinical trials for diabetic complications, with, in general, rather disappointing results. Indeed, it remains to be fully defined as to which pathways in diabetic complications are essentially protective rather than pathological, in terms of their effects on the underlying disease process. Furthermore, seemingly independent pathways are also showing significant interactions with each other to exacerbate pathology. Interestingly, some of these pathways may not only play key roles in complications but also in the development of diabetes per se. This review aims to comprehensively discuss the well validated, as well as putative mechanisms involved in the development of diabetic complications. In addition, new fields of research, which warrant further investigation as potential therapeutic targets of the future, will be highlighted.

Anti-inflammatory therapy in type 1 diabetes

Type 1 diabetes (T1D) is a multi-factorial, organ-specific autoimmune disease in genetically susceptible individuals, which is characterized by a selective and progressive loss of insulin-producing β-cells. Cells mediating innate as well as adaptive immunity infiltrate pancreatic islets, thereby generating an aberrant inflammatory process called insulitis that can be mirrored by a pathologic autoantibody production and autoreactive T-cells. In tight cooperation with infiltrating innate immune cells, which secrete high levels of pro-inflammatory cytokines like IL-1β, TNFα, and INFγ effector T-cells trigger the fatal destruction process of β-cells. There is ongoing discussion on the contribution of inflammation in T1D pathogenesis, ranging from a bystander reaction of autoimmunity to a dysregulation of immune responses that initiate inflammatory processes and thereby actively promoting β-cell death. Here, we review recent advances in anti-inflammatory interventions in T1D animal models and preclinical studies and discuss their mode of action as well as their capacity to interfere with T1D development.

Insights into type 1 diabetes provided by genetic analyses

PURPOSE OF REVIEW

Recent identification of over 60 loci contributing to the susceptibility of developing type 1 diabetes (T1D) provides a timely opportunity to assess what is currently known of the genetics of T1D, and what these discoveries may tell us about the disease itself.

RECENT FINDINGS

The major findings will be discussed under five main themes: T1D risk gene identification, molecular mechanisms of susceptibility, shared genetic cause with other diseases, development of novel analytical methods, and understanding disease heterogeneity.

SUMMARY

The plethora of T1D risk genes that have been identified risk overwhelming clinicians with lists of gene names and symbols that have little bearing on management, and provide a challenge for researchers to place the genetics of T1D in a more amenable clinical context.

Identification of haplotype tag single nucleotide polymorphisms within the receptor for advanced glycation end products gene and their clinical relevance in patients with major trauma

INTRODUCTION

The receptor for advanced glycation end products (RAGE) has been considered as one of the major pattern recognition receptors and plays an important role in the development of sepsis and multiple organ dysfunction in critical illnesses. Although genetic variants of the RAGE gene have been shown to be well associated with susceptibility to some inflammatory diseases, little is known about their clinical relevance in the development of sepsis in critical ill patients.

METHODS

Four genetic variants were selected from the entire RAGE gene and genotyped using pyrosequencing and polymerase chain reaction-length polymorphism methods. Association studies were performed in two independent Chinese Han populations.

RESULTS

Among the four genetic variants, only the rs1800625 polymorphism was significantly associated with sepsis morbidity rate and multiple organ dysfunction (MOD) scores in patients with major trauma both in Chongqing (n = 496) and Zhejiang (n = 232) districts, respectively. Results from ex vivo responsiveness of peripheral blood leukocytes indicated that the rs1800625 polymorphism was well associated with decreased production of TNFα. In addition, the rs1800625 polymorphism could significantly inhibit the promoter activities of the RAGE gene.

CONCLUSIONS

The rs1800625 polymorphism is a functional variant, which might be used as a relevant risk estimate for the development of sepsis and multiple organ dysfunction syndrome in patients with major trauma.

A meta-analysis of receptor for advanced glycation end products gene: four well-evaluated polymorphisms with diabetes mellitus

Genetic association studies on the gene encoding receptor for advanced glycation end products (RAGE) and diabetes mellitus have reported conflicting results. To evaluate the association of RAGE gene four widely-evaluated polymorphisms (T-429C, T-374A, Gly82Ser and G1704T) and diabetes mellitus, a meta-analysis was conducted. A random-effects model was applied irrespective of between-study heterogeneity. There were a total of 5808/3742 (n=14) case-patients/controls (studies) for T-429C, 8259/6935 (n=19) for T-374A, 7029/5266 (n=19) for Gly82Ser, and 2843/3302 (n=13) for G1704T. Overall results detected no significant association of polymorphisms T-429C, T-374A and Gly82Ser with diabetes risk. There was a trend toward an increased risk for alleles 1704T relative to 1704G (odds ratio [OR]=1.09; 95% confidence interval [CI]: 0.98-1.22; I(2)=0). Subgroup analysis by ethnicity indicated that allele 1704T conferred a significantly increased risk in East Asians (OR=1.21; 95% CI: 1.04-1.4; I(2)=0) but not in Caucasians (OR=0.8; 95% CI: 0.6-1.07; I(2)=0), and that by type of diabetes mellitus indicated that association was potentiated exclusively for G1704T with diabetic retinopathy (OR=1.24; 95% CI: 1.01-1.51; I(2)=0). No publication bias was observed. Our results provide convincing evidence regarding the association of RAGE gene 1704T allele with an increased risk of diabetes mellitus, especially diabetic retinopathy. Notably, this effect was more pronounced in East Asians.

Multiwalled carbon nanotubes induce a fibrogenic response by stimulating reactive oxygen species production, activating NF-κB signaling, and promoting fibroblast-to-myofibroblast transformation

Carbon nanotubes (CNTs) are novel materials with unique electronic and mechanical properties. The extremely small size, fiberlike shape, large surface area, and unique surface chemistry render their distinctive chemical and physical characteristics and raise potential hazards to humans. Several reports have shown that pulmonary exposure to CNTs caused inflammation and lung fibrosis in rodents. The molecular mechanisms that govern CNT lung toxicity remain largely unaddressed. Here, we report that multiwalled carbon nanotubes (MWCNTs) have potent, dose-dependent toxicity on cultured human lung cells (BEAS-2B, A549, and WI38-VA13). Mechanistic analyses were carried out at subtoxic doses (≤20 μg/mL, ≤ 24 h). MWCNTs induced substantial ROS production and mitochondrial damage, implicating oxidative stress in cellular damage by MWCNT. MWCNTs activated the NF-κB signaling pathway in macrophages (RAW264.7) to increase the secretion of a panel of cytokines and chemokines (TNFα, IL-1β, IL-6, IL-10, and MCP1) that promote inflammation. Activation of NF-κB involved rapid degradation of IκBα, nuclear accumulation of NF-κBp65, binding of NF-κB to specific DNA-binding sequences, and transactivation of target gene promoters. Finally, MWCNTs induced the production of profibrogenic growth factors TGFβ1 and PDGF from macrophages that function as paracrine signals to promote the transformation of lung fibroblasts (WI38-VA13) into myofibroblasts, a key step in the development of fibrosis. Our results revealed that MWCNTs elicit multiple and intertwining signaling events involving oxidative damage, inflammatory cytokine production, and myofibroblast transformation, which potentially underlie the toxicity and fibrosis in human lungs by MWCNTs.

Advanced glycation end products are direct modulators of β-cell function

OBJECTIVE

Excess accumulation of advanced glycation end products (AGEs) contributes to aging and chronic diseases. We aimed to obtain evidence that exposure to AGEs plays a role in the development of type 1 diabetes (T1D).

RESEARCH DESIGN AND METHODS

The effect of AGEs was examined on insulin secretion by MIN6N8 cells and mouse islets and in vivo in three separate rodent models: AGE-injected or high AGE-fed Sprague-Dawley rats and nonobese diabetic (NODLt) mice. Rodents were also treated with the AGE-lowering agent alagebrium.

RESULTS

β-Cells exposed to AGEs displayed acute glucose-stimulated insulin secretory defects, mitochondrial abnormalities including excess superoxide generation, a decline in ATP content, loss of MnSOD activity, reduced calcium flux, and increased glucose uptake, all of which were improved with alagebrium treatment or with MnSOD adenoviral overexpression. Isolated mouse islets exposed to AGEs had decreased glucose-stimulated insulin secretion, increased mitochondrial superoxide production, and depletion of ATP content, which were improved with alagebrium or with MnTBAP, an SOD mimetic. In rats, transient or chronic exposure to AGEs caused progressive insulin secretory defects, superoxide generation, and β-cell death, ameliorated with alagebrium. NODLt mice had increased circulating AGEs in association with an increase in islet mitochondrial superoxide generation, which was prevented by alagebrium, which also reduced the incidence of autoimmune diabetes. Finally, at-risk children who progressed to T1D had higher AGE concentrations than matched nonprogressors.

CONCLUSIONS

These findings demonstrate that AGEs directly cause insulin secretory defects, most likely by impairing mitochondrial function, which may contribute to the development of T1D.